<i>L</i>-Arginine and <i>L</i>-Nitroarginine Methylester Effects on Vasomotion in Isolated Rabbit Eyes

Abstract

Background/Aims: Although nitric oxide (NO) has been shown to be essential for maintaining the basal blood flow in the retina and optic nerve head, its exact role in vasomotion is still controversial. This study investigated L-arginine (L-Arg) and N-nitro-L-arginine methylester (L-NAME) effects on vascular reactivity in a model of isolated rabbit eye. Methods: Rabbit external ophthalmic arteries (n = 12) in a head-mounted preparation were cannulated and perfused with warmed Tyrode solution. The effect of intraluminal pressure as a measure of total vascular resistance was assessed. Response curves to intra-arterial injections of 3 growing concentrations of L-Arg (n = 6) and L-NAME (n = 6) were obtained. Results: Without any drug administration, spontaneous oscillations were observed in all the models. L-Arg (NO precursor) induced vasodilation and decreased both frequency and amplitude of the periodic oscillations. L-NAME (NO synthase inhibitor) produced a strong vasoconstrictor tone and stimulated vasomotion, causing a faster rate of pulsatility. Conclusion:L-Arg and L-NAME acted as modulators of ocular vascular tone. L-Arg elicited vasodilation and decreased vasomotion while L-NAME produced a strong vasoconstrictor tone and caused a faster rate of pulsatility. These findings justify the need to investigate NO precursors and antagonists as possible alternative therapeutics in vascular eye diseases.

Extracellular l-arginine Enhances Relaxations Induced by Opening of Calcium-Activated SKCa Channels in Porcine Retinal Arteriole

“…This is also supported by the observations that l -arginine uptake, rather than the intracellular l -arginine concentration, is important for NO production in endothelial cells [25]. Indeed, in isolated rabbit eyes, administration of l -arginine decreases ocular vascular tone [26], supporting a major role for l -arginine uptake and NO release in endothelium-dependent relaxation in retinal arterioles.…”

Myogenic Oscillations in Rabbit Ocular Vasculature Are Very Low Frequency

“…In the decomposition of the signal obtained in the ex vivo models, there were no bands present in the HF or LF region due to abolition of autonomic influences, so the myogenic vascular responses were due to autoregulatory mechanisms as has been demonstrated elsewhere [13,14,15]. …”

Spontaneous High Frequency Diameter Oscillations of Larger Retinal Arterioles Are Reduced in Type 2 Diabetes Mellitus

“…These spontaneous diameter changes have been shown in all tissues hitherto studied, including the choriocapillaris, 4 and both in vivo and in vitro studies in the retina have shown that the phenomenon depends on NO-induced synthesis of cyclic guanosine monophosphate (GMP). [5][6][7] The accompanying oscillations in oxygenation have been recorded both in the retina 7 and in the optic nerve. 9,10 Vasomotion has been found to be disturbed outside the eye in patients with diabetes mellitus, 11 and disturbances in vasomotion has been proposed to be involved in the pathogenesis of diabetic retinopathy.…”